U.S. Pat. No. 4,298,025, which is owned by the present assignee, discloses a control valve for use in water softeners having two resin tanks. One of the resin tanks is normally on-line while the other tank is regenerated and placed in a standby condition until the first tank requires regeneration. The disclosed control valve controls which of the tanks is on-line and controls the regeneration sequence of an exhausted tank.
The quantity of water treated by a given tank, is monitored by a mechanism that includes a water usage turbine driven by water entering the on-line resin tank. When a predetermined quantity of water is treated, which produces to a predetermined number of revolutions in the turbine, a regeneration sequence is initiated which places the standby tank on-line and isolates the exhausted tank.
A second turbine, operatively connected to a regeneration sequence control element (in the form of a disk) is rotated by a stream of water that is activated at the beginning of the regeneration cycle. The stream of water physically drives the regeneration control disk (via the turbine and associated drive train) through its sequence. With the disclosed arrangement, the frequency of regeneration of the water softener system is determined by the usage turbine which directly measures the quantity of fluid treated by a given tank.
In U.S. Pat. No. 4,427,549 which is also owned by the present assignee, a deionization method and apparatus is disclosed. The disclosed apparatus includes a control valve similar to the control valve disclosed in U.S. Pat. No. 4,298,025 in that it includes a usage turbine for monitoring the amount of source water treated by a given tank and a regeneration control turbine for driving a control element through a regeneration sequence.
In U.S. application Ser. No. 083,721 filed Aug. 10, 1987 under the title Apparatus and Method for Recovering Materials from Process Baths, a method and apparatus for recovering a metal such as nickel from a plating bath is disclosed. A control valve similar in function to the control valve disclosed in U.S. Pat. Nos. 4,298,025 and 4,427,549 can be used to control an apparatus embodying the invention of U.S. Ser. No. 083,721, if a pair of resin tanks are employed, one of which is on-line, the other of which is regenerated and held off-line.
In all three of the above described fluid treatment and related applications, the regeneration frequency is determined by a quantity of fluid treated by the system. In selecting the frequency (i.e., the quantity of fluid to be treated before regeneration is necessary), it is assumed that the characteristics of the fluid to be treated remain fairly constant. In case of a water softener system, it is assumed that the water to be softened contains a fairly constant concentration of minerals to be removed. In the case of a deionization system, it is assumed that the incoming fluid has a fairly constant concentration of cations and anions. In the case of a metal recovery system, it is assumed that the fluid being processed has a fairly constant concentration of the metal to be recovered.
As a practical matter, however, in some applications the characteristics of the incoming fluid vary. As a result, the frequency of regeneration, as determined by the water usage turbine, may be excessive resulting in the waste of regeneration chemicals, or may occur at insufficient intervals which cause the quality of the output fluid to degrade.
Systems have been suggested in which the frequency of regeneration of an ion exchange bed is a function of a monitored characteristic or parameter in the output fluid. For example in U.S. Pat. No. 2,938,868 which issued to Carlson et al., a method of controlling regeneration of ion exchangers is disclosed that includes an apparatus for monitoring the output of a deionization apparatus. In the system disclosed in this patent, the pH or alternately, the conductivity of the effluent is monitored and when the pH (or the conductivity) of the effluent reaches a predetermined level, regeneration of the anion and/or cation beds is initiated.
In many industrial applications which use deionized water, relatively high quality water is required and the high quality level must be maintained throughout the operation of the deionization system. It has been found, that by monitoring the effluent, the quality of the output must degrade at least slightly in order for the system controller to recognize that regeneration is required. It has also been found that it is desirable to regenerate a resin bed before it is fully exhausted. By regenerating a resin bed prior to complete exhaustion, it has been found that extremely high-quality deionized water can be maintained throughout the operation of the deionization apparatus. Devices that rely on the degradation in quality of the output stream in order to effect regeneration of the resin bed have proved unsatisfactory in those applications that require high quality deionized water.